1. Field of the Invention
This invention relates to hydrostatic bearings in which a shaft and the static bearing to be fitted on the shaft are rotatable or slidable relative to one another, and more particularly to a hydrostatic bearing utilizing a ferromagnetic fluid as a working fluid.
2. Description of the Prior Art
There has been proposed a hydrostatic bearing of a conventional type as shown by FIG. 12.
This conventional type bearing comprises a rotary shaft 2 fitted within a hydrostatic bearing 1. The inner face of the hydrostatic bearing 1 is provided with an oil chamber 3 supplied with working oil under a predetermined pressure, annular recovering grooves 4 disposed at both axial ends of the bearing spaced apart at a predetermined distance, and a pair of sealing grooves 5, each of which is also disposed at both axial extremities of the bearing. The oil chamber 3 is supplied with the working oil from an exterior oil pump 7 through a vent port 6. Working oil axially squeezed out from the oil chamber 3 is recovered from the recovering grooves 4 and returned to an oil tank 9 via a vent port 8. The sealing groove 5 is supplied with hydrostatic sealing gas from a pressurized sealing gas source 10 via a pressure regulating valve 11 and a port 12 so that the operating oil squeezed out of the recovery grooves 4 can be prevented from escaping.
U.S. Pat. No. 3,439,961 discloses a bearing entitled "Bifluid Hydrodynamic Bearing" which uses a high pressure gas as a hydrostatic gas and seals the operating high pressure gas by magnetically attracting a ferromagnetic fluid containing fine ferrite particles by means of a magnetizing coil.
However, since the conventional bearing as shown by FIG. 12 is constructed in such a manner that the working oil is prevented from escaping by keeping the pressure balance between the working oil and the sealing fluid, it becomes impossible to shut out the hydrostatic system from the exterior atmosphere. Additionally, another problem is that such air sealing cannot be applied to such facilities for making semiconductors which must be carried out in a vacuum.
It was contemplated to use a mechanical seal in place of an air seal with an intention to obviate such drawbacks, but in this way it was inevitable that some extent of air exists around the sealing means in the oil recovering means as a shock absorbing medium so as to maintain the sealing function of the device when the hydrostatic bearing is started, at the time of load variation and against thermal expansion, and therefore, it is also inevitable that a slight extent of seal gas may be squeezed out.
Moreover, roller bearings instead of hydrostatic bearings have also been used, however, such bearings require grease as a lubricant and the oil contained in the grease may evaporate and thus contaminate the outer atmosphere.
The bearing of U.S. Pat. No. 3,439,961 is constructed to seal the high pressure gas by a ferromagnetic fluid, but because of the high extent of compressibility of the high pressure gas used as a hydrostatic fluid as compared with liquid, it cannot be used since it is not possible for such bearing to supplement high pressure gas during running, so it would not be able to function as a hydrostatic bearing when some extent of high pressure gas has been squeezed out due to long periods of use.
An object of the present invention has been set by taking the problems encountered in the aforesaid prior art bearings into consideration, and it aims to provide a hydrostatic bearing using ferromagnetic fluid which can solve the above-mentioned problems by virtue of utilizing noncompressive ferromagnetic fluid as the working fluid of a hydrostatic bearing and by preventing this ferromagnetic fluid from escaping outside of the bearing.
Another object of the present invention is to provide a hydrostatic bearing utilizing ferromagnetic fluid capable of improving the efficiency of impelling the ferromagnetic fluid by providing suitable impelling means for returning the ferromagnetic fluid to the fluid chamber of the bearing.